The fabrication of certain types of heat exchangers requires welding a plurality of heat exchange tubes to end sheets, referred to herein as tube sheets. Welding the heat exchange tubes to tube sheets requires forming a circular weld joint at the location where the tube ends pass through the tube sheets. Typically, each tube end is flush with the outer surface of the tube sheet and the weld joint is formed at that location to rigidly affix each tube to the tube sheets and to create a seal. Welders for such applications are known in the art. Typically, such welders are very expensive and complicated in structure and operation since the welds being formed are subject to relatively high pressures and their integrity is critical. In some applications, however, the heat exchanger is not subject to high pressure during use, and thus the integrity and seal of the weld joint is less of a concern. Thus, for certain applications, there has developed a need in the art for a welder apparatus for forming circular weld joints which is relatively inexpensive, yet provides satisfactory results.